Recent trends in the detergents market are towards fabric washing powders which are denser than hitherto. The reasons for this are partly due to reduced packaging costs and partly due to an improved washing performance because consumers tend to dispense washing powders by volume rather than by weight. The majority of washing powders are presently manufactured by a spray-drying process and this tends to produce powders of relatively low bulk density, that to say is typically less than 500 g/liter. The bulk density is very dependent on the amount and type of active detergent present in the powder during the spray-drying operation.
The commonly used anionic detergents, sodium alkyl sulphates and sodium alkyl aryl sulphonates, are particularly prone to produce light powders.
It has been discovered that powders with higher bulk densities can be obtained if part of the active detergent is sprayed onto the spray-dried powders rather than incorporated into the slurry before spray-drying. However, in order to be suitable for spraying onto the powders, the active detergents (surfactants) must be sufficiently mobile at temperatures below about 80.degree. C. to be atomised effectively.
GB No. 1 579 261 (Colgate-Palmolive Co) relates to processes for converting various liquid or liquefiable detergents into detergent powders by spraying those surfactants onto spray-dried builder beads. The specification refers to synthetic detergents such as nonionics, anionics and cationics or conbinations thereof as in general being liquid or liquefiable. In our experience, so far as mixtures of aqueous anionic and nonionic surfactants are concerned, these mixtures are viscous gels which can only be oversprayed onto particulate absorbents if they are heated to a temperature, typically above 90.degree. C., at which they become sufficiently mobile. That is severely disadvantageous in factory practice.
EP No. 88 612A (Bridgemace) discloses mobile liquid detergents containing not more than 8% water and not less than 90% active detergent, including an anionic surfactant, a nonionic polyether, and coconut mono- or diethanolamide. Substantial quantities of the third ingredient (at least 20% in every Example, about 33% being apparently preferred) are required in order to obtain sufficiently mobile liquid products.
GB No. 1 169 594 (Unilever) discloses liquid detergent compositions comprising ammonium alkylbenzenesulphonate and a nonionic detergent. The compositions are prepared by passing ammonia through a mixture of alkylbenzenesulphonic acid and nonionic detergent.
We have now discovered a range of compositions comprising anionic surfactant, nonionic surfactant and water which are sufficiently mobile at temperatures no higher than 80.degree. C. to enable them to be sprayed onto absorbents.